It is known that one of the main problems of those electronic equipment that have to provide for the amplification of signals of small amplitude is caused by the background noise that limits the minimum signal that is possible to amplify.
The noise may be reduced by means of an accurate design and, even more, by paying attention to the energy source, i.e. to the power supply circuit.
Usually, all power supplies obtained by the mains voltage generate noise and interference, which limit the resolution of the electronic amplification equipment.
This phenomenon can be immediately noticed in audio equipment and it's the reason why sophisticated filtering circuits are used to reduce the noise due to the power supply.
Another solution for reducing said noise consists of the use of batteries or accumulators, that brings good results but has evident drawbacks. All interference due to the mains are eliminated; as since there are no rectification circuits, together with the mains injected noise also the band switching noise of the rectification diodes is eliminated.
From the tests performed on the use of the above power supply, a phenomenon appears though, that might be linked to the electrochemical reaction time or to the used materials, and said phenomenon is clearly audible in the audio field:                small signals relative to the high frequency harmonics, are not reproduced with the correct phase or are even cut off;        in terms of quality of listening, the ambience gets lost,        this phenomenon is audible in the reproduction as well as in the recording phase, and affects the ambience which is one of the most important parameters in the sound reproduction.        
In alternative, it is possible to turn to generators like dynamos or alternators for obtaining an energy source that is not connected to the mains and it's not of electrochemical nature, but said generators comprise moving parts, are noisy and require a constant control of their operation.